This invention relates to a method for separating rubber components and filler components from a vulcanized rubber or an unvulcanized rubber by liquidifying the vulcanized rubber or the unvulcanized rubber at normal temperature and normal pressure; and a method for separating structural members from a rubber composite material.
This invention also relates to a reusable rubber and a reusable carbon black recovered by such separation method; and a rubber composition containing such rubber or such carbon black. More specifically, this invention relates to a recovered rubber having excellent physical properties which has been obtained by treating a waste rubber composition by a particular method; a rubber composition having such recovered rubber blended therein; a recovered carbon black having excellent physical properties which has been obtained by treating a waste rubber composition by a particular method, and a rubber composition having such recovered carbon black blended therein.
Furthermore, this invention relates to a method for producing a carbon black which, when blended in a vulcanized rubber; exhibits extremely low value of loss tangent (tan xcex4) at 60xc2x0 C. which is an index for low fuel cost of the tire; such carbon black; and a rubber composition and a vulcanized rubber containing such carbon black.
Disposal of industrial wastes has nowadays become a serious social problem, and in the case of tires, the amount discarded is enormous and not only use as a fuel by incineration but also recovery and reuse of the raw materials included in the tire, namely, the rubber and the rubber subsidiary materials has become an urgent agenda. A rubber, however, is quite stable once it has vulcanized due to its crosslinked structure, and the rubber has been insoluble at room temperature in ordinary solvents, and at most, swellable to some extent in such solvents.
One process known in the art for the recovery of the rubber, carbon black, and other rubber subsidiaries from vulcanized rubber wastes is recovery of the rubber as a gaseous or liquid hydrocarbon by thermal decomposition of the vulcanized rubber. For example, JP-A 60-40193 discloses recovery of the rubber as a liquid hydrocarbon by thermal decomposition of used tires, cable wastes, or other vulcanized rubber wastes together with wastes of polyethylene, polypropylene or the like at a temperature of 150 to 500xc2x0 C. and a pressure of 20 to 800 bar, and in the presence of a solvent. JP-A 7-310076 discloses a method for obtaining a decomposed oil having a reduced sulfur content wherein a vulcanized rubber is thermally decomposed to obtain a hydrocarbon (a gaseous product) and a decomposed oil containing carbon black (slurry-like product) and wherein the thermal decomposition is conducted in the presence of a hydrogen-donating solvent such as tetralin.
Also proposed are a method wherein direct or indirect heating is conducted at a high temperature of, for example, at least 500xc2x0 C.; a method wherein the thermal decomposition is conducted in the presence of a solvent, a catalyst and hydrogen (U.S. Pat. No. 3,704,108); a method wherein the thermal decomposition is conducted in the presence of a molten salt (European Patent No. 71789, U.S. Pat. No. 3,996,022), and the like.
Such recovery of the rubber materials and subsidiaries from vulcanized rubber products by the thermal decomposition requires an enormous cost for installation when such recovery is to be conducted in an industrial scale, since a high temperature, high pressure thermal decomposition apparatus is required for the thermal decomposition.
A method for plasticizing vulcanized rubber powder is disclosed in Journal of Japan Rubber Association 49 (1976) page 829. In this method, various types of sulfur-vulcanized rubbers in the form of a powder having a particle diameter of up to 2 mm are immersed in carbon tetrachloride or toluene in the presence of benzoyl peroxide at a rubber powder (mg)/toluene (ml) ratio of 500/7 to 500/2 to thereby promote decomposition in the liquid by air oxidation at a temperature of 70 to 100xc2x0 C.
This method, however, was an attempt to regenerate the vulcanized rubber by plasticizing the vulcanized rubber under heating, and re-vulcanizing and adding the plasticized reaction product in the fresh rubber. The article of Journal of Japan Rubber Association also described that the vulcanized rubber containing no carbon black was more susceptible to oxidative decomposition than the vulcanized rubber containing carbon black. In view of the situation that carbon black is blended in most commercially available industrial rubbers, this method is not very useful. In addition, the vulcanized rubber regenerated from the reaction product of the oxidative decomposition reaction exhibited inferior physical properties when the ratio of the re-vulcanized rubber to the fresh rubber was high.
When the rubber materials and subsidiaries are recovered from the vulcanized rubber product by the thermal decomposition as described above, substantially all of the rubber components in the vulcanized rubber are converted into low molecular weight hydrocarbons (C4-benzene, C4-cyclohexane, etc.). Main use of the thus recovered hydrocarbon has been used as a light fuel at the furthest, and such hydrocarbon could not be reused as a starting material of the rubber composition since the starting rubber is required a certain high molecular weight.
The disposal of industrial wastes is not a problem restricted to vulcanized rubber products, and scraps produced in kneading and processing as well as other unvulcanized scrap rubbers inevitably generated in the production of the vulcanized rubber products have also become a serious problem. In view of such situation, recovery of rubber materials and subsidiaries, and efficient reuse of such materials are also an important issue.
In the typical production of a rubber product such as tire, the starting rubber is first masticated, and the thus softened rubber is then admixed with a filler, a softener, a vulcanizer, a vulcanization accelerator, an antiaging agent and the like. The mixture is then kneaded, molded in an extruder of the like, vulcanized, and formed into products by appropriate processing. As is well known, a large amount of unvulcanized scrap rubber is inevitably produced in the course of such steps. Exemplary such unvulcanized scrap rubbers include rubber scraps discarded in the steps of mastication and kneading due to early vulcanization or uneven vulcanization (burned spot or scorching), and defective rubbers discarded in the step of vulcanization due to the so called sagging, and there are various types of the scrap rubbers depending on their production process including the one wherein vulcanized and unvulcanized parts are intermingled, and the one wherein steel member or organic fiber member is attached.
The issue of industrial waste disposal has recently become a quite serious social problem, and with regard to the unvulcanized scrap rubbers discharged from factories, it has been conceived that, not only the incineration of the unvulcanized scrap rubbers as fuels, but also the recovery of the starting rubber and rubber subsidiary materials and their efficient reuse are important.
Therefore, in the disposal of such unvulcanized scrap rubbers, complicated preliminary steps of sorting the scrap rubbers by their types, and removing members comprising steel or organic fibers as well as vulcanized portions have been conducted, and the recovery of the rubber for reuse in other rubber products has been only limited and most scrap rubbers have been discarded.
In view of such situation, if a method capable of separating structural members by liquidifying the vulcanized rubber composition at room temperature or at a relatively low temperature under normal pressure, or a method wherein a vulcanized rubber composition can be separated into the rubber component and the filler component at room temperature or at a relatively low temperature under normal pressure were realized, installation such as thermal decomposition apparatus or heating apparatus will no longer be necessary and simple, convenient recovery of the rubber materials and subsidiaries from the vulcanized rubber products at low cost will be enabled, and such recovery has great industrial applicability. More specifically, if a rubber component which can withstand the reuse can be separated and recovered from the rubber waste in general, and the rubber composition having the recovered rubber blended therein exhibits particular set of properties necessary for the highly demanded rubber composition, such method has high industrial applicability.
The situation is the same for unvulcanized rubbers. If structural members could be separated from unvulcanized scrap rubbers or the unvulcanized scrap rubber could be separated into the rubber component and the filler component with no complicated preliminary steps of sorting the scrap rubbers by their types or removing the members comprising steel or organic fibers as well as vulcanized portions, and with no thermal decomposition, heating, or other installation, a simple, convenient recovery of the rubber materials, and subsidiaries from the unvulcanized scrap rubbers at low cost will be available, and such recovery has great industrial applicability.
With regard to the recovered carbon black, the carbon black which has been recovered by thermal decomposition at a high temperature of 500xc2x0 C. or higher as described above is mostly inferior in its quality compared to the carbon black which has been used as a starting material. Accordingly, reuse of carbon black has been deemed difficult, and no carbon black which can be used in practice has so far been obtained.
On the other hand, the substance that has been recovered by thermal decomposition at a relatively low temperature of about 400xc2x0 C. in the presence of a solvent or a catalyst was a substance comprising a mixture of oil, rubber and carbon black, and separation of such components was difficult.
As described above, the situation is the same for carbon black. If a reusable carbon black of high purity which has a quality equivalent or better than the carbon black that has been used for the staring material could be recovered from any rubber waste with no thermal decomposition, heating, or other installation and at room temperature or at a relatively low temperature under normal pressure, and the rubber composition produced by incorporating such recovered carbon black had particular set of physical properties which is required for the highly demanded rubber composition, such carbon black has great industrial applicability.
For example, there is recently a growing need for a rubber composition having high damping property, namely, high hysteresis, which is capable of converting the vibration into heat to thereby reduce seismic energy. The rubber composition having such properties can be used, for example, in a seismic energy absorbing member which is rapidly becoming common, namely, in seismic isolation which is used for seismic resistance, vibration control, bridge bearing, or basic isolation of buildings in order to protect bridges and buildings from earth quakes by reducing the seismic acceleration.
Improvement in rolling resistance of automobile tires has also been long awaited as a means for reducing energy loss during the drive to thereby improve fuel economy. The rolling resistance of a tire can be evaluated by using loss tangent at 50xc2x0 C. to 70xc2x0 C. (typically tan xcex4 at 60xc2x0 C.) for the index, and a rubber composition which can be produced into a vulcanized rubber exhibiting a low tan xcex4 value at 60xc2x0 C.
A tire has a large amount of carbon black incorporated therein for the purpose of reinforcement, and influence of the carbon black on abrasion resistance, mechanical strength, rubber properties and other properties of the tire is considerable. However, it is not easy to blend the carbon black for the purpose of reinforcement and maintain the rubber properties, and simultaneously, improve the fuel economy.
Solutions for such problem by improving surface activity of the carbon black have been proposed. In an exemplary such method, focus is on hydrogen content and oxygen content of the carbon black, and their ratio, H/O is increased to at least 0.20 to thereby improve the fuel economy while retaining the abrasion resistance (JP-A 10-36703).
In another method, the method as described above is described as being insufficient in improving the fuel economy, and adjustment of oxygen content, concentration of weakly acidic group, concentration of basic functional group, and amount of rubber physically adsorbed of the carbon black into a particular range is proposed and such adjustment is accomplished by oxidizing hard carbon black with nitric acid, hydrogen peroxide, ozone or other strong oxidizing agent, or by oxidizing the carbon black by blowing water or steam into the reaction furnace and incorporating oxygen-containing functional group onto the surface of the carbon black to thereby increase the oxygen content, and thereafter heat treating the carbon black at a temperature of 1000xc2x0 C. to 1500xc2x0 C. (JP-A 11-60800).
JP-A 11-60800 discloses that the SBR rubber composition having such carbon black incorporated therein (Example) exhibited a tan xcex4 value at 60xc2x0 C. lower than that of the SBR rubber composition having the untreated carbon black incorporated therein (Standard Sample), and that the reduction in the value compared to the Standard Sample was 6 to 8%.
There is, however, still a demand for the rubber composition exhibiting even lower value of tan xcex4 at 60xc2x0 C.
The present invention has been accomplished in view of the situation as described above, and an object of the present invention is to provide a method for separating the structural member from a rubber composite material by dispersing the vulcanized rubber composition in the form of small pieces in a solvent, or by dissolving the vulcanized rubber composition in an organic solvent at room temperature and normal pressure; and a method for separating the rubber component and the filler component in a vulcanized rubber composition.
Another object of the present invention is to provide a simple, convenient method which is capable of separating structural members, or rubber components or filler components, from unvulcanized rubber composite materials and unvulcanized rubber compositions discarded mainly from factories as not being put into market, by means of a particular treatment irrespective of their form (whether they are integrated with other structural member, or whether they are hard or soft), and preferably with no preliminary separation.
Further object of the present invention is to provide a rubber composition which can be recovered from any rubber composition and which can be reused as a starting rubber in producing rubber compositions, and which enables production of rubber compositions of favorable properties when blended in the rubber composition.
Still further object of the present invention is to provide a carbon black which can be recovered from rubber compositions and which has unique feature which are not found in the carbon black used as the raw material; and a rubber composition containing such rubber composition which exhibits excellent damping properties.
Still further object of the present invention is to provide a carbon black which can be recovered from rubber compositions and which has a quality equivalent or better than that of the carbon black used as the raw material; and a rubber composition produced by incorporating such recovered carbon black which exhibits excellent physical properties.
Still further object of the present invention is to provide a method for producing a carbon black which maintains the rubber properties of the vulcanized rubber and which has retained the reinforcement action of a carbon black, and which has enabled to reduce the loss tangent (tan xcex4) at 60xc2x0 C. by an unexpectable degree; the carbon black produced by such method; and the rubber composition and the vulcanized rubber containing such carbon black.
The inventors of the present invention have made an extensive study in search of a simple, convenient method capable of recovering rubber materials and structural members from a vulcanized rubber product at a low cost without using any thermal decomposition apparatus or heating apparatus, and then found that, when blocks of rubber composite material or vulcanized rubber composition are immersed in a large amount or organic solvent containing a small amount of a peroxide at normal temperature and normal pressure, the vulcanized rubber composition can be liquidified in the solvent and the filler component and the structural member can be separated. The first aspect of the present invention according to 1 to 13 as described below was thereby completed.
1. A method for separating a rubber composite material containing a vulcanized rubber composition and at least one structural member other than the vulcanized rubber composition wherein the rubber composite material is immersed in an organic solvent containing 0.01 to 50% of a peroxide with or without agitation to liquidity the vulcanized rubber composition for separation of the structural member, wherein said immersion is conducted such that the ratio of the rubber composite material (mg)/the organic solvent (ml) is up to 100.
2. A method for separating the rubber composite material according to the above 1 wherein said immersion with or without agitation,is conducted at a temperature of 0 to 40xc2x0 C.
3. A method for separating the rubber composite material according to the above 1 or 2 wherein said rubber composite material is in the form of a block having at least one edge exceeding 2 mm.
4. A method for separating the rubber composite material according to any one of the above 1 to 3 wherein said separation is conducted by centrifugation, membrane separation, or decantation.
5. A method for separating the rubber composite material according to any one of the above 1 to 4 wherein said peroxide is selected from the group consisting of benzoyl peroxide, t-butyl hydroperoxide, diisopropylbenzene hydroperoxide, p-methane hydroperoxide, cumene hydroperoxide, and azobisisobutyronitrile.
6. A method for separating the rubber composite material according to any one of the above 1 to 5 wherein said vulcanized rubber composition is a vulcanized rubber composition containing at least 1 part by weight of carbon black and/or silica per 100 parts-by weight of the rubber component.
7. A method for separating a vulcanized rubber composition containing a vulcanized rubber and, at least, a filler wherein said vulcanized rubber composition is immersed in an organic solvent containing 0.01 to 50% of a peroxide with or without agitation to liquidify the vulcanized rubber composition for separation of the rubber component and the filler component in the vulcanized rubber composition, wherein said immersion is conducted such that the ratio of the vulcanized rubber composition (mg)/the organic solvent (ml) is up to 30.
8. A method for separating a vulcanized rubber composition containing a vulcanized rubber and, at least, a filler wherein the vulcanized rubber composition is immersed in an organic solvent containing 0.01 to 50% by weight of a peroxide with or without agitation to liquidify the vulcanized rubber composition for separation of the rubber component and the filler component in the vulcanized rubber compositions wherein said immersion is conducted such that the ratio of the vulcanized rubber composition (mg)/the organic solvent (ml) is up to 30, and wherein said method further comprises the steps of removing the separated filler component from the reaction system and adding further organic solvent to the reaction system.
9. A method for separating the vulcanized rubber composition according to the above 7 or 8 wherein said immersion with or without agitation is conducted at a temperature of 0 to 40xc2x0 C.
10. A method for separating the vulcanized rubber composition according to any one of the above 7 to 9 wherein said vulcanized rubber composition is in the form of a block having at least one edge exceeding 2 mm.
11. A method for separating the vulcanized rubber composition according to any one of the above 7 to 10 wherein said separation is conducted by centrifugation, membrane separation, or decantation.
12. A method for separating the vulcanized rubber composition according to any one of the above 7 to 11 wherein said peroxide is selected from the group consisting of benzoyl peroxide, t-butyl hydroperoxide, diisopropylbenzene hydroperoxide, p-methane hydroperoxide, cumene hydroperoxide, and azobisisobutyronitrile.
13. A method for separating the vulcanized rubber composition according to any one of the above 7 to 12 wherein said vulcanized rubber composition is a vulcanized rubber composition containing at least 1 part by weight of carbon black and/or silica per 100 parts by weight of the rubber component.
The inventors of the present invention also made an extensive study in search of a simple, convenient method capable of recovering rubber materials and structural members from an unvulcanized scrap rubber at a low cost without using any thermal decomposition apparatus or heating apparatus, and then found that, when unvulcanized rubber composite material or unvulcanized rubber composition is immersed in an organic solvent containing a peroxide at normal temperature and normal pressure, the unvulcanized rubber composition can be liquidified in the solvent and the filler component and the structural member can be separated irrespective of the size, location, degree of crosslinking of the vulcanized portion in the unvulcanized scrap rubber. The second aspect of the present invention according to 14 to 21 as described below was thereby completed.
14. A method for separating an unvulcanized rubber composition comprising an unvulcanized rubber and at least a filler wherein the unvulcanized rubber composition is immersed in an organic solvent containing 0.01 to 50% by weight of a peroxide with or without agitation to liquidity the unvulcanized rubber composition for separation of the rubber component and the filler component in the unvulcanized rubber composition.
15. A method for separating the unvulcanized rubber composition according to the above 14 wherein said unvulcanized rubber composition is immersed in said organic solvent at a ratio of the unvulcanized rubber composition (mg)/the organic solvent (ml) of up to 30.
16. A method for separating an unvulcanized rubber composition containing an unvulcanized rubber and, at least, a filler wherein the unvulcanized rubber composition is immersed in an organic solvent containing 0.01 to 50% by weight of a peroxide with or without agitation to liquidity the unvulcanized rubber composition for separation of the rubber component and the filler component in the unvulcanized rubber composition, wherein said immersion is conducted such that the ratio of the unvulcanized rubber composition (mg)/the organic solvent (ml) is up to 30, and wherein said method further comprises the steps of removing the separated filler component from the reaction system and adding further unvulcanized rubber composition and/or organic solvent to the reaction system.
17. A method for separating the unvulcanized rubber composition according to any one of the above 14 to 16 wherein said immersion with or without agitation is conducted at a temperature of 0 to 40xc2x0 C.
18. A method for separating the unvulcanized rubber composition according to any one of the above 14 to 17 wherein said unvulcanized rubber composition is in the form of a block having at least one edge exceeding 2 mm.
19. A method for separating the unvulcanized rubber composition according to any one of the above 14 to 18 wherein said separation is conducted by centrifugation, membrane separation, or decantation.
20. A method for separating the unvulcanized rubber composition according to any one of the above 14 to 19 wherein said peroxide is selected from the group consisting of benzoyl peroxide, t-butyl hydroperoxide, diisopropylbenzene hydroperoxide, p-methane hydroperoxide, cumene hydroperoxide, and azobisisobutyronitrile.
21. A method for separating the unvulcanized rubber composition according to any one of the above 14 to 20 wherein said unvulcanized rubber composition is an unvulcanized rubber composition containing at least 1 part by weight of carbon black and/or silica per 100 parts by weight of the rubber component.
The inventors of the present invention also developed a simple, convenient method capable of recovering the rubber component and the filler component of a vulcanized rubber composition separately at a low cost without using any thermal decomposition apparatus or heating apparatus, and when the liquid component recovered by such separation method was analyzed, it was unexpectedly found that a liquid rubber having a high molecular weight has been separated, and the rubber composition having such liquid rubber incorporated therein exhibits a hysteresis and loss tangent (tan xcex4) higher than the rubber composition having a starting rubber generally used as starting material incorporated therein. It was also found that the recovered rubber having such superior properties can be obtained not only from the vulcanized rubber composition, but also from unvulcanized rubber composition such as the unvulcanized scrap rubber inevitably produced in the process of producing vulcanized rubber product. The third aspect of the present invention according to 22 to 25 as described below was thereby completed.
22. A recovered rubber by immersing a rubber composition in an organic solvent containing 0.01 to 50% by weight of a peroxide with or without agitation to decompose said rubber composition, wherein said recovered rubber contains up to 5% by weight of decomposition product of said peroxide.
23. A recovered rubber by immersing a rubber composition in an organic solvent containing 0.01 to 50% by weight of a peroxide with or without agitation to decompose said rubber composition and subjecting the liquid product to a heat treatment at 100xc2x0 C. to 160xc2x0 C. for 5 minutes to 30 minutes, wherein said recovered rubber contains up to 5% by weight of decomposition product of said peroxide.
24. A recovered rubber according to the above 22 or 23 wherein said peroxide is benzoyl peroxide and said organic solvent is toluene.
25. A rubber composition containing the recovered rubber of any one of the above 22 to 24, and a rubber and/or a resin.
The inventors of the present invention also developed a simple, convenient method capable of recovering rubber component and the filler component of a vulcanized rubber composition separately at a low cost without using any thermal decomposition apparatus or heating apparatus, and when the carbon black recovered by such separation method was analyzed for the physical properties, it was unexpectedly found that the rubber composition having such carbon black incorporated therein exhibits unique properties and the rubber composition having such carbon black incorporated therein exhibits superior damping properties higher than the rubber composition having a starting rubber generally used as starting material incorporated therein. It was also found that the recovered carbon black having such superior properties can be obtained not only from the vulcanized rubber composition, but also from unvulcanized rubber composition such as the unvulcanized scrap rubber inevitably produced in the process of producing vulcanized rubber product. The fourth aspect of the present invention according to 26 to 29 as described below was thereby completed.
26. A recovered carbon black by decomposing a rubber composition containing at least a rubber and a carbon black.
27. A recovered carbon black according to the above 26 wherein said decomposition is conducted by immersing the rubber composition in an organic solvent containing 0.01 to 50% by weight of a peroxide with or without agitation to decompose said rubber composition, wherein said immersion is conducted such that the ratio of the rubber composition (mg)/the organic solvent (ml) is up to 30.
28. A recovered carbon black according to the above 27 wherein said peroxide is benzoyl peroxide and said organic solvent is toluene.
29. A rubber composition containing the recovered carbon black of any one of the above 26 to 28, and a rubber and/or a resin.
The inventors of the present invention also found that a rubber composition exhibiting low loss tan xcex4 at 60xc2x0 C. can be produced by subjecting the starting carbon black to a heat treatment under particular conditions, and the fifth aspect of the present invention according to 30 to 39 as described below was thereby completed.
30. A method for producing a carbon black comprising the step of heat-treating a virgin carbon black in a non-oxidizing atmosphere at a temperature of 300xc2x0 C. to 1500xc2x0 C. for at least 30 seconds in the presence of at least one rubber compound component selected from rubber and a vulcanization aid.
31. A method for producing the carbon black according to the above 30 wherein a vulcanizer is further comprised as a rubber compound component.
32. A method for producing the carbon black according to the above 30 or 31 wherein said virgin carbon black and said rubber compound component are mixed in an organic solvent to prepare a mixture solution followed by removal of said organic solvent, and the resulting dry product is subjected to said heat treatment.
33. A method for producing the carbon black according to any one of the above 30 to 32 wherein said rubber is a diene rubber.
34. A method for producing the carbon black according to any one of the above 30 to 33 wherein said vulcanization aid is zinc oxide and/or stearic acid.
35. A method for producing the carbon black according to any one of the above 30 to 34 wherein said vulcanizer is at least one member selected from sulfur, an organic peroxide, and a vulcanization accelerator.
36. A method for producing the carbon black according to any one of the above 30 to 35 wherein said method further comprises the step of producing a starting virgin carbon black.
37. A carbon black produced by the method for producing the carbon black of any one of the above 30 to 36 wherein said carbon black is capable of producing a rubber composition having a tan xcex4 lower than the rubber composition produced by substituting the carbon black with a virgin carbon black of equivalent blend ratio.
38. A rubber composition containing the carbon black of the above 37.
39. A vulcanized rubber obtained from the rubber composition of the above 38.
The inventors of the present invention also found that the poor quality of the conventional recovered carbon black which has been recovered by heat treating a vulcanized rubber composition can be improved by conducing the heat treatment under predetermined conditions. To be more specific, the inventors found that, heat treatment was insufficient in the conventional recovery process since the process was conducted in an industrial scale by an industrial method wherein the vulcanized rubber composition of a large amount was treated at once; that the solid product recovered by decomposition of the vulcanized rubber composition or from the unvulcanized rubber composition itself can be sufficiently heat treated such that the amount of the organic components on the surface of the carbon black is equivalent or less than the amount of the organic components on the surface of a virgin carbon black normally employed as the starting material; and unexpectedly, that the rubber composition having incorporated such recovered carbon black therein has higher tensile strength (modulus) and lower loss tangent (tan xcex4) compared to the rubber composition having a virgin carbon black normally employed as the starting material incorporated therein. It was also found that the recovered carbon black having such superior properties can be obtained not only from the vulcanized rubber composition, but also from the solid product recovered by decomposition of the unvulcanized scrap rubber or other unvulcanized rubber composition inevitably produced in the process of producing vulcanized rubber product, or from the unvulcanized rubber composition itself. The sixth aspect of the present invention according to 40 to 43 as described below was thereby completed.
40. A recovered carbon black produced by heat-treating a solid recovered from a rubber composition containing at least a rubber and carbon black in a non-oxidizing atmosphere at a temperature of 300xc2x0 C. to 1500xc2x0 C. for at least 30 seconds, wherein amount of organic components on the surface of said carbon black is equivalent to or less than the amount of organic components on the surface of a virgin carbon black used for the starting material of the rubber composition.
41. A recovered carbon black according to the above 40 wherein said solid product has been recovered by immersing the rubber composition in an organic solvent containing 0.01 to 50% by weight of a peroxide with or without agitation, and wherein said immersion has been conducted such that the ratio of the rubber composition (mg)/the organic solvent (ml) is up to 30.
42. A recovered carbon black according to the above 31 wherein said peroxide is benzoyl peroxide and said organic solvent is toluene.
43. A rubber composition containing the recovered carbon black of any one of the above 30 to 32, and a rubber and/or a resin.